Characterizing thin film PV devices with Low-Incidence Surface Milling by Focused Ion Beam

Abstract

We used Low-Incidence Surface Milling by Focused Ion Beam (LISM-FIB) at glancing incident angle from the film surface to expose complete structures of thin-film CdTe device for scanning electron microscopic (SEM) investigation. Specific sample preparation procedures of this method are described. This method enables observation of micro-features in the thickness dimension of thin film devices in a planar view for various microscopic studies, particularly electron microscopy. We have observed that a ~52 nm thick buffer layer in Pilkington TEC glass is extended to approximately 1 µm from the top view in SEM. We also provide two consistent methods for identifying the exposed layers. An interesting feature of a porous layer of ~100 nm at CdTe side of the CdS/CdTe junction has been observed for the first time. Impacts of such a layer on thin CdTe PV devices are discussed.

Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties

“…Despite the ubiquity of FIB, however, concomitant ion implantation, amorphization, and undesired surface topography remain persistent challenges [1,20,21]. Of course, approaches to mitigate this damage have been developed, including protective masks and finishing steps with FIM employing low beam energies, low currents, and low-incidence (grazing) angle surface milling [22,23]. However low dose exposure still causes topographic swelling, stippling, and mechanical damage [24], or interferes with electrical properties [25,26].…”